The present invention is generally directed to the operation and configuration of computer system consoles in a multicomputer complex. Additionally, in support of console message services, the present invention also includes a distributed shared memory structure which permits "multiple read/multiple write" (MRMW) operation protocols.
To more fully appreciate the present invention, it is appropriate to have an understanding of the environment in which it functions. In particular, the environment is most readily considered to be a multicomputer environment which is loosely coupled by means of a shared memory unit which typically comprises a direct access storage device (DASD). Additionally, it is contemplated that the present invention operates in an environment in which the computers in the complex are also connected together and are able to transmit and receive data separately via physical links which are typically represented herein as channel to channel adapters (CTCAs).
As indicated above, there are two aspects of the present invention. The first aspect involves a distributed shared memory discipline and structure which permits multiple read and multiple write operation protocols across a multicomputer complex. This aspect of applicants' invention is generic and is not limited by the environment described immediately above. However, in another aspect of the present invention, applicants have employed a distributed shared memory system structure in the context of providing improved console communications between computer systems in a multicomputer complex.
A key problem addressed by the present applicants is the simultaneous access and sharing of data among a plurality of users in a computer system complex. In particular, users, through their user written applications, often wish to have access to the same set of data at the same time. This includes the necessity and/or desire to be able to read the data and to write to the same data set (file). Implementation of distributed shared memory systems and structures often follows two diverse constructs. In one construct data migration is employed. In this schema, data is "owned" by only one user at a time and either the data itself or "ownership" of the data is passed from user to user or system to system. In the other construct, data replication is employed. That is to say, multiple copies of the data are maintained and each local user is permitted to read and write to the data set via utilization of a central sequencing mechanism to ensure data consistency. This sequencing (or queueing) is necessary if one wants to ensure that all write operations to the data have been done before read operations are undertaken so that users accessing of the data have the most recent information available. One major aspect of the present invention, is that each system or user in the complex has the immediate authority to write to replicated data set without the necessity of employing a distributed server system. In particular, in order to achieve this functionality, the present invention employs a peer-to-peer communication protocol rather than a master/slave protocol system.
In the other aspect of the invention, a distributed shared memory mechanism is applied to system operator console functioning as a mechanism for the transmission of messages to selected console devices. In this context, a message transmitter may be a computer operator working at a specific system complex control console. The message sender may in fact be a user or equivalently a user written application running in one of the address spaces on one of the computer systems in the complex.
In prior systems, it was difficult to manage the whole system from a single one or even a common set of system operator consoles. However, by a judicious application of a distributed shared memory system, it is now possible for messages generated on any computer system in the complex to be viewable by any other console in the complex. Moreover, operating system commands may be directed to any system in the complex. Furthermore, it is possible to provide unique identification for commands which send messages to the computer operator even though the commands to do so are generated on different systems in the complex. This enables a reply command to be issued from any system to answer the specific "Write To Operator with Reply" (WTOR) command. Additionally, message redirection, via either specific commands or events, is carried out by sending updates to the messages instead of transmitting or retransmitting the messages themselves around the computer complex. This provides significant efficiencies. As a result, each system has a common view of operating system services as a result of control by a system of control blocks that are distributed and maintained in a distributed shared fashion across the computer complex.